1. Field of the Invention
This invention relates to a radiotherapy apparatus, more particularly to a radiotherapy apparatus having a radioactive ray generating mechanism using a high energy electron beam, and more particularly to a radiotherapy apparatus suitable for treating a point of a patient's body by applying radioactive rays to it in an optional direction.
2. Description of the Prior Art
A device to generate radioactive rays by using an electron beam that is accelerated to high energy by an accelerator so as to use the radioactive ray for treating has generally a construction as shown in FIG. 5. That is, an electron beam 2 is irradiated to a target 5 in a radiation head for generating radioactive rays so as to generate a radioactive ray 6 from the target 5. Such a radioactive ray generator is fixed on a radiating head 10 in general. Therefore, a change of a radiating direction or a radiated position of a radioactive ray is made by rotation of a gantry 11 and movement of a treating table 9. However, there is a problem of poor freedom of radiating directions, and as described in Japanese Patent Laid-Open Publication No. 55-83900, a radiating head can be turned around the gantry 11.
In order to radiate a radioactive ray to a point in the patient's body from optional directions, in the conventional radiotherapy apparatus it is necessary to operate the radiating head and the treating table in a complex way, and thus it is difficult to maintain the high accuracy which is required by actual medical treatment. Moreover, so as to apply a radioactive ray to a point of the patient's body from optional directions, an apparatus is known in which many radioactive ray generators using radioactive cobalt are fixedly arranged on a spherical surface, but there is a very troublesome problem in the keeping and handling of cobalt because of its radioactivity. It is desirable to radiate a radioactive ray generated by an electron beam to a point of the patient's body in an optional direction.